The Oblong Box, 1969 Britain
Directed by Gordon Hessler
Starring Vincent Price, Christopher Lee and Alister Williamson.
This was the first film to star both Price and Lee.
The Oblong Box explores and combines several Edgar Allan Poe themes, such as premature burial and masked figures, combined with new elements, including voo-doo rituals/killings.
Synopsis from IMDb: Aristocrat Julian Markham keeps his disfigured brother, Sir Edward, locked in a tower of his house. Sir Edward occasionally escapes and causes havoc around the town.
There are also problematic flashbacks related to the time the brothers spent on their plantation in Africa, and how one incident with their slaves and a case of mistaken identity led to a voodoo ritual that would change both brothers' lives forever.
From Wikipedia: Price, Davies and Dwyer had recently appeared in Witchfinder General, under the direction of Michael Reeves, and on 18 November 1968, the four also began work on the Oblong Box. The original script had the Markham brothers as twins, both played by Vincent Price.
Christopher Wicking was bought in to do some additional dialogue. He says AIP were keen to put the film into production to take advantage of Witchfinders success and that they had also promised him When the Sleeper Wakes and a film about Christ coming to the modern day. Wicking says Oblong Box "was the carrot".
However, Reeves fell ill during pre-production, so Hessler stepped in and made a number of substantial changes.
The Oblong Box contains enough content inspired by Edgar Allan Poe to qualify it as one of the American International "Poe films", but it was not directed by Roger Corman, and therefore is only considered an honourable mention in the Corman-Poe cycle. It reminded me somewhat of a fusion between a Hammer Film (perhaps because of the large number of British actors, including Hammer stalwart, Christopher Lee) and Corman-Poe cycle film The Haunted Palace, which combines themes and styles of Poe and Lovecraft. So, here again, we see Poe themes combined with other themes--not Lovecraft related, but still of interest during the late 60s--though, again, be prepared for some out of date and problematic content involving African characters. At least they had Black actors playing the parts--it could always be worse.
Some fun tidbits of trivia from IMDb: